Canker Sore or Fever Blister: What’s the difference?

mouth dental ulcerWhen you notice a painful sore in or around your child’s mouth, you may find yourself wondering when it’s time to be concerned. When is a bump, blister, or sore a normal occurrence, and when should you contact your pediatric dentist for help?

Two of the most common oral irritations, canker sore (apthous ulcers) and cold sores (sometimes called fever blisters) can look very similar, and they can be equally uncomfortable and annoying. These lesions are quite different, however, and it’s important to differentiate between the two in order to ensure that your child receives the most effective treatment.

Location, Location…

A canker sore or apthous ulcer is a painful round lesion that is often red and white, occurring on the soft tissue lining inside of the mouth. These may develop with no prior warning and they usually involve the insides of the cheeks, the gums, or the tongue.

A fever blister or cold sore typically develops along the outside border of the lips, the firm (non-moveable) part of the gum tissue, and the roof of the mouth. These lesions may look like fluid-filled
blisters that will eventually burst and then heal with a scab.

What causes it?

Research suggests that canker sores are related to an abnormality in the immune system, though no specific cause has been determined. These ulcers tend to be triggered by hormonal changes, stress, illness, nutritional deficiencies, allergies, and traumatic injuries, but may also occur for no apparent reason at all.

Fever blisters are specifically caused by the herpes simplex virus type 1 (HSV-1), which is transmitted through bodily fluids (even saliva) from one person to another. An initial herpes infection is typically accompanied by a fever, sore throat, nausea, swelling, and painful sores. As the lesions heal and then reappear, the onset may be preceded by a tingling, itching or burning, 1-2 days before the blisters appear.


Canker sores will generally go away without any treatment. However, if they are preventing your child from eating, drinking, or speaking, schedule a dental appointment right away for a palliative solution.

Fever blisters can often be controlled with antiviral medications, though they are very contagious, so it is wise to limit kissing and sharing food or drinks during this time. If the blisters become more persistent or problematic, don’t hesitate to contact your pediatric dentist right away.